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She has taken excessively high dose of Doxycycline as for her age. I would recommend in such case to skip the dose for next 2-3 days. And if she has any loose stools, gastritis , or acidity then she would require to take a Probiotic containing Lactobacillus and a combination of Pantoprazole and Domperidone. Doxycycline frequently causes stomach upset. So, in case she has, follow the mentioned advice, else just skip the dose for next 3 days, and re start again as has been advised by your doctor.
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